Energy saving in the working environment is essential to build a green world and is increasingly enforced by regulations. In some working environments, such as manufacturing environments, robots are used to improve productivity. Human workers work along with these robots during particular times of the day. At other times, the robots operate without the presence of human workers.
Working space requirements may be (very) different for human workers and robots. For example, human workers require and appropriate amount of light in order to have proper vision to perform their jobs, whereas robots may operate under low light conditions or even completely in the dark. Other requirements, such as ventilation and heating requirements, may differ between human workers and robots as well.
In order to control space elements responsible for setting the conditions in the working space, detectors may be used in the working space to determine whether or not human workers are present. When human workers are detected, the space elements are controlled to fulfill the working requirements (e.g. illumination and/or temperature) for human workers in the working space. When no human workers are detected, the space elements are controlled to set the working space conditions such that the optimum amount of energy is saved provided that the robots can still operate appropriately under those conditions.
Although motion sensors have been developed which could detect movements by detecting heat signals, ultrasonic signals or microwave signals, these sensors cannot distinguish between human workers and robots.
In addition to controlling working space conditions, another application requiring appropriate distinction between human beings and other objects includes intrusion control of the space. Intrusion control relates to safety conditions set for a working place.
Document U.S. Pat. No. 6,384,414 discloses a method and apparatus for detecting the presence of an object using one or more passive thermal radiation sensors, wherein thermal radiation from an object at a first wavelength and a second wavelength is detected. The signals are compared to a threshold condition that indicates whether an object is an intruder. The method and apparatus are said to enable differentiating humans from other objects or from other types of emitters.
The prior art method and apparatus use radiation properties of objects to judge whether an object is human or not. Although this works well if there is only one object in front of the sensors, in case of multiple moving objects in the environment the sensors only measure the mean temperature, making it difficult to decide on the presence of a human being. For example, the average temperature of a cool machine object and a hot machine object may be close to human temperature. Accordingly, to discriminate between human movements in factory workshops with a lot of background noise and other object movement, it is difficult to achieve a high hit rate and low false alarm simultaneously using radiation properties only.
Thus, there is a need in the art for an improved detection system capable of distinguishing between human objects and other objects, particularly machine-type objects.